This is my current build http://forums.afterdawn.com/thread_view.cfm/737374 But was wondering if this PSU would be powerful enough to power it? http://www.newegg.com/Product/Product.aspx?Item=N82E16817371005
Yes plenty. My file server uses the 380W Earthwatts and uses an E4300 (uses 10W more than an E5200), an X1900XT (uses 60W more than an HD4670) and six hard drives instead of one. It will be fine.
Think of a cross between a spare older PC and a giant external hard disk, but connected over a network.